Typing in the raw path field fired one /api/gitroot probe per
keystroke (#74). The draft now schedules the probe 250ms out — matching
GITROOT_PROBE_DEBOUNCE_MS in web/src/spawnForm.ts — and every keystroke
resets it; the 30Hz heartbeat polls for due probes so the burst's one
request fires after typing stops. The seq guard in resolve_gitroot is
untouched, so a late answer still cannot overwrite a newer input.